This application claims the benefit of Japanese Application No. 9-138779, filed in Japan on May 28, 1997, which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an optical pickup device for an optical recording and reproducing apparatus, such as an optical disc player.
2. Discussion of the Related Art
An optical disc player, which can reproduce recording information from a recording media such as a laser disc (LD), a compact disc (CD) or a digital video (or versatile) disc (DVD), is well known. A so-called compatible disc player, which can reproduce recording information from those different types of optical discs, is also known.
In such a disc player, an optical pickup device has an optical system for irradiating a light beam onto an optical disc and reading a return light from the optical disc. Japanese patent publication JP-B-2-8379 discloses an example of the optical pickup device utilizing a diffraction grating formed on a transparent parallel flat plate for beam deflection and guiding. As shown in FIG. 11, the optical pickup device has a light beam from a light source 1 focused on a pit train formed on an information recording surface 5 of an optical disc by an objective lens 4. The return light reflected from the information recording surface 5 again passes through the objective lens 4, is deflected by a diffraction grating formed on a parallel flat plate 25, and is guided and focused onto four light-receiving elements of a photodetector 6.
In the optical pickup device described above, the four light-receiving elements of the photodetector 6 are divided and arranged parallel and perpendicular to the direction of the information track of the disc. Accordingly, when astigmatism is generated by the diffraction grating on the parallel flat plate 25, the direction of an astigmatism axis coincides with a direction of dividing lines of the four light-receiving elements, and a focus error signal cannot be detected. When the four light-receiving elements are inclined to a certain degree, a tracking error signal may interfere with the focus error signal. Namely, when the return light is detected for controlling the position of the light beam relative to an information track on the information recording surface, an overlap of the detecting surface and the track direction, or a land border, causes the interference of the detection signal.
Accordingly, the present invention is directed to an optical pickup device that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to use a hologram optical element to improve the quality of the focus error signal.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, in one aspect of the present invention there is provided an optical pickup device including a photodetector divided into four light-receiving elements by two dividing lines, an incident optical system for irradiating a light beam onto an optical recording medium, and a receiving optical system for guiding a return light from the optical recording medium to the photodetector, wherein the receiving optical system includes astigmatism generating means for generating astigmatism having an astigmatism axis at an angle of 45 degree with respect to the two dividing lines.
In another aspect of the present invention there is provided an optical pickup device including a light source for irradiating an incident light beam onto an optical recording medium, a photodetector having four light-receiving elements for receiving a return light beam from the optical recording medium, and a light deflecting device positioned in a forward light path between the light source and the optical recording medium and in a return light path between the optical recording medium and the photodetector, wherein the light deflecting device passes the incident light beam and deflects the return light towards the photodetector.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.